Manganese alloys



Patented May 29, 1945 MANGANESE ALLOYS Reginald S. Dean, Salt Lake City, Utah, assignor to Chicago Development Company, Chicago, Ill., a corporation of Illinois I No Drawing. Application July 12, 1941, I Serial No. 402,239

9 Claims.

' My invention relates to'the preparation and heat treatment of alloys consisting essentially of manganese, iron and chromium, wherein the chromium content is in excess of the manganese content, and is particularly concerned .with the preparation of such alloys which are highly resistant to atmospheric corrosion, possess the ability to withstand great extensionby cold work without the hardening which is characteristic of austenitic stainless steels and irons heretofore known in the art, and, in addition, have the property of being hardened, without embrittlement, by heat treatment. I

Alloys of manganese, chromium and iron, in which the chromium content exceeds the mangaeffect on the hardness or produces a softening, depending upon the rate at which the alloys werecooled in casting.

It will be seen, therefore, as hereinafter pointed out in detail, that, by a suitable selection of alloy compositions and by heating of the alloys to approximately 1200 degrees C. and cooling or nese content, have heretofore been suggested but,

in all cases, those alloys whose properties have been investigated have contained a substantial content of carbon, of the order of 1% or more, although suggestions have been made for alloys where the carbon content was allegedly zero.

There has, however, been no suggestion in the,

prior art of the amenability of such alloys to said heat treatments nor of the usual characteristics which are brought about by the heat treatments which are set out hereinafter in detail. Other alloys have been suggested in the prior art which contain manganese, chromium and iron, both carbon and silicon being present and the silicon comprising in excess of 3% and up to 8%.

The alloys of my invention are sharply distinguishable from those of the prior art in composi- I tion as well a in physical characteristics and properties. Thus, for example, the alloys of my invention must be substantially entirely free from the oxides of silicon and aluminum, carbon is substantially, and preferably entirely, absent, and silicon should not exceed 1% and is preferably present in amounts less than 0.7 and particularly close to 0%.

Again, there is a very definite and radical difference between the heat treatment proposed by involves heating the cast" alloy to 1000 de rees quenching, I may cold-work the said alloys, by rolling, swaging or by any other means, to a very substantial extent without excessive hardening. By excessive hardening, I refer to any hardness above about 25 as measured on the Rockwell C. scale. I have found that the range of alloy composition in which this phase of my invention may be practiced may be defined approximately as follows: From 7.5% to 22.5% manganese, from 15% to 32% chromium, the chromium content always exceeding the manganese content, and the balance being substantially all iron. A preferred range of the constituents of my alloys is 10 to 20% maganese, 24 to 30% chromium, balance iron.

As I have indicated hereinabove, when the alout undue hardening makes the alloys highly cooling at a rate such that at least six hours is required for the alloy to. reach room temperature after the heat is turned off. It will be understood, of course, that the length of time required to bring the temperature of the heated alloy down to room temperature during the slow cooling process will depend, in part, upon the size and shape of the alloy element being treated. It

will also be understood that the slow cooling may ,be carried out in ahalthough, for/best results, it

should be carried out man inert atmosphere.

I have also found that the alloys of my invention may eflectivelybe placed in condition for extensive cold work by quenching them, preferably in water, from about 1 200 degrees C. This treatment malge thamloysislightly harder than does the slow cooling modes but renders them more susceptible 'to subseq ent hardening by heat treatinent'.-

Independently of whic of the two methods described hereinabove is employed to treat the alloys prior to the orking thereof, I have discovered that, y r heating the cold worked alloy'to temper e between about 400 degrees C. and 800 degrees C.,,substa'ntial hardening takes place. In certain instances, this hardening may I be brought to ashigh as Rockwell C. 59. In those bf the alloys of my invention which contain not more than about 18% manganese, the alloys do not appear to become brittle by heating at any temperature within the aforementioned range. 7

When the alloys contain or upwards of manganese, embrittlement sometimes occurs by heating to temperatures of 550 degrees C. to 600 degrees C. Valuable hardness characteristics, how,- ever, may be developed in these latter alloys by utilizing lower hardening temperatures. I

3 The following examples are illustrative of alloys falling within the scope of my present invention. It will be understood that various changes may be made therein, in the light of the guiding principles 7 which I have disclosed, without in any manner hardness of the alloy was Rockwell C 53.. On'

heating for a further period of two hours at 700 degrees C., the hardnesswas Rockwell C 59.v

Even in this extremely hard condition, the alloy was remarkably tough. 1 l

I Emample 2 I a High. purity electrolytic iron, electrolytic chromium and electrolytic manganese, were melted together to produce an alloy of 10% manganese, chromium, balance iron. vOn heating said alloy to 1200 degrees C, and quenching and then reducing by cold work to the extent of 75% reduction in area, the hardness of the alloy was 18 on the Rockwell .0 scale. on reheating the quenched and cold worked alloy to a temperatureof 600 degrees C, for two hours, the hardness increased to Rockwell C 31. An additional two hours at 650 degrees C. increased the hardness to Rockwell C 46 and a still further two hours at 700 degrees 0. increased the hardness to Rockwell C- 53.

Example 3 1 Highpurity electrolytic iron, chromium and I manganese were melted together to produce an alloy containing 19% manganese, 20% chromium, balance iron. Said alloy, when quenched from 1200 degrees'C. and severely cold worked, had

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a Rockwell Chardness of 21. On reheating for two hours at 600 degrees 0., the hardnessor the alloy. became Rockwell C 51. An additional heating. of the alloy for two'hours at 700 degrees C..

inc'reased'the hardness to Rockwell C53.

' Example 4' High purity electrolytic iron, chromium alloy containing 20% manganese, 24% chromium, balance iron. This alloy, when quenched from and i manganese were melted together to produce an 120 0 degrees C. and severely cold worked, had a Rockwell C hardness of 24. On reheating to a temperature of 550 degrees -C., the alloy had a hardness of Rockwell C 55.

In the practice of my invention. I prefer to employ electrolytic iron, electrolytic chromiuni I and electrolytic manganese of high purity so as not to introduce deleteriousconstituents into the alloys. I have found, for example, that the presence of oxides of aluminum and silicon, such as l are present in silico-thermic or alumino-thermic manganese or ferro-manganese prevents the efiective practice of my invention. While the g5 manganese which I employ may be produced by 1 a vacuum distillation process, I prefer, particu- I larly, to employ electrolytic'manganese having a purity of at least about 99.0% and'preterably of 99.9%..

By virtue of their hardening by reheating after 1 quenching, particularly with intermediate cold work, my alloys are particularly useful foryarious purposes as, for example, gears, bearings, armour plate, and for purposes, in general, where casehardened nickel or nickel-chromium steels have 1 heretofore been used. The alloys of my present invention, hardened as described herein, have a wide utility in articles of cutlery, ball and rollerbearings, tools and dies, especially saws, and other 40 tools which are necessarily exposed to corrosive influences. In thersoft state, the alloys ofmy present invention may be employed for cooking utensils and other purposes where a relatively i soft material of satisfactory working qualities and a high degree of stainlessnessis desired.

They may alsobe utilized in the aircraft and automotive industries such as for the manufacture of thin sheets, of very high strength, for the fabrication of airplane wings or the like.

What- I'claim as new and desire to protect by Letters Patent of the United States is: 1. A process of producing stainless alloys of iron, chromium and manganese in the form of I greatly cold worked rods, sheet. or wire which 5 comprises selectin'g an alloy within the composition range 7.5 to 22.5 per cent manganese, 15 to 32 per cent chromium, the chromium content always exceeding the manganese content, the balance being substantially ,all iron, heating said and subjecting the same to extensive cold work.

2. A process of producing stainless alloys of 0 alloy to approximately 1200 degrees C., cooling,

1 iron, chromium and manganese in a hardened but not brittle state and in, a form obtained by a relatively large amount of cold work, which com prises selecting an alloy of iron, manganese and chromium within the composition range.7.5 to j 22.5 per cent manganese, 15 to 32 per cent chromium, the percentage of chromium always exceeding that of the manganese, balance substantially all iron, heating said alloy to not substantially less than 1200 degrees C., cooling saidalloy, extensively cold working said alloy, and then hardening by. heating to a temperature between 400 degrees and 800 degrees C.

3. A process of producing stainless alloys of iron, chromium and manganese in a hardened but not brittle state and in a form obtained by a relatively large amount of cold work, which comprises selecting an alloy of iron, manganese and chromium within the composition range 7.5 to 18 per cent manganese, 16 to 30 per cent chromium, the chromium always exceeding the manganese, balance substantially all iron, heating said alloy to approximately 1200 degrees C., quenching said alloy, extensively cold working said alloy, and then hardening by heating to temperatures between 400 degrees and 800 degrees C.

4. A process of producing thin sheets oi. stainless alloys of iron, chromium and manganese in a hardened state which comprises selecting an alloy from the composition range 10 to 20 per cent high purity manganese, 24 to 30 per cent high purity chromium, balance substantially all high purity iron, heating such alloy to approxi- .mately 1200 degrees C., cooling, cold rolling said alloy to the desired dimensions, and reheating said alloy to a temperature between 400 degrees C. and 800 degrees C.

5. Stainless alloys consisting essentially of manganese, chromium and iron, substantially entirely free of. carbon and of oxides of aluminum and silicon, said alloys being in hardened form resulting from cooling from approximately 1200 degrees C., extensively cold working, and reheating between about 400 degrees C. and 800 degrees 0., the alloy constituents being present in substantially the following proportions: 7.5 to 22.5 per cent of manganese, 15 to 32 per cent of chromium, the chromium content always exceeding that of the manganese, and balance substantially all iron.

6. Stainless alloys, in the form thin sheets,

of oxides of aluminum and silicon, said alloys being in hardened form, resulting from cooling from approximately 1200 degrees C., rolling into sheet form, and reheating within the range of about 400 degrees C. to 800-degrees C., the alloy constituents being present in substantially the following proportions: 7.5 to 22.5 per cent of manganese, to 32 per cent of chromium, the chromium content always exceeding that of the manganese, and balance substantially all iron.

'IJA cold worked alloy consisting essentially of iron, chromium, and manganese, said ,alloy having a hardness of not more than on the Rockwell C scale and resulting from heating said alloy to approximately 1200 degrees C. and cooling, said alloy containing from 7.5 to 22.5% manganese, from 16 to chromium, balance substantially all iron, the chromium content being always in excess of the manganese content, said alloy being substantially entirely free from carbon and oxides of silicon and aluminum.

consisting essentially ot manganese, chromium and iron, substantially entirely tree of carbon and 8. A hardened alloy of iron, chromium and manganese, said alloy being made from high purity metals and containing from 7.5 to 22.5% manganese, from 16 to 32% chromium, the chromium content always exceeding the manganese content, balance substantially all iron, said alloy having been cooled from about 1200 degrees C.,

severely cold worked, and reheated to a temperature between 400 and 800 degrees C.

9. A hardened alloy of iron, chromium and manganese, said alloy being made from high purity metals and containing from 10 to 20% manganese, from 24 to 30% chromium, balance substantially all iron, the hardening of said alloy resulting from heating the same to approximately 1200 degrees C., quenching in water, and reheating to an eleva d temperature.

REGINALD S. DEAN. 

